A multiplexer is used in transmitting data signals over a fiber-optic conductor, e.g. from a computer to a fiber cable and between the fiber cable and the terminals. A plurality of data channels which may be synchronous or asynchronous are transferred via the cable between the user terminals and the computer in both directions. In such a case, the multiplexer shall convert the parallel asynchronous data flow from computer/user to the fiber cable so that a serial data flow is obtained in the cable.
It is known in the art to over-sample and encode the incoming data channels for multiplexing a plurality of incoming asynchronous and parallel data channels to a serial bit flow. Over-sampling, means that the data signals are sensed several times per bit slot with the aid of a high-frequency clock. Jitter is introduced on the data channels due to the data signals and clock not being asynchronous. This jitter can, however, be made optically small by sufficiently great oversampling.
The serial bitflow is encoded after the parallel-series conversion. It is desirable to give the serial bit flow an even d.c. balance i.e. equally as many logical 1's as 0's before electro-optical conversion and transmission over the fiber channel. Sensitive receivers are namely a.c.-circuited. Scrambling or block encoding is carried out for this pupose.
Other problems in transmitting over fiber cables is the obtainment of a strong synchronizing condition, possibility of self-correction and small time delay.
The above-mentioned conventional solution with parallel-series conversion, self-correcting encoding and d.c. balancing will generally be a very expensive solution, particularly since decoding on the receiver side is carried out in a corresponding manner, namely descrambling (or block decoding), self-correction and series-parallel conversion.
An example of a system in the art using a special encoding method in transmission over an optical fiber is given in the U.S. Pat. No. 4,249,266, which does not utilize over-sampled data, however.